The efficacy of metoprolol as an antihypertensive agent was assessed in 20 previously untreated Asian patients with mild to moderate hypertension. After a 4-week run-in period when placebo therapy was given, the patients were given oral metoprolol at a starting dosage of 100 mg twice daily. The dosage of metoprolol was increased at fortnightly intervals until either satisfactory blood pressure control, defined as a diastolic blood pressure of less than 90 mmHg or a greater than 10% fall in pre-treatment diastolic blood pressure, was achieved or a total of 400 mg metoprolol was reached. All 20 patients had satisfactory control of their blood pressures on a twice-daily regimen and the average dosage of metoprolol required was 200 mg daily. For the second part of the study, the medication was changed to a once-daily regimen at the same total dosage of metoprolol. Final efficacy of once-daily therapy was assessed after 8 weeks of treatment. All blood pressure and pulse rate reductions were significant (P < 0.001) from the placebo phase. However, twice-daily and once-daily readings were not significantly different from each other. No side-effects were reported during the study.